Heh, well, not so much the funniest movie, but i definitely had an ex girlfriend (read: psycho.) that got REALLY pissed off when she saw i had my eyes open one time when we were making out... because i wasn't "in love." Thanks Heartbreakers!

Shaun of the Dead is probably the best in my opinion. Witty humor combined with perfect satire and parody, all wrapped with hilarious characters and a great style of filming. Hot Fuzz and Run Fatboy Run are also great and with a similar sense of humor/cast.

Tropic Thunder was quite hilarious too. Saw it twice in theaters and was "lol"ing both times.

Well you see it's a generational thing, some classic ' funny ' movies might be hilarious to some and so-so to others.
Nothing against newcomers like tropic thunder or rush hour 3 ( I loved both very much by the way ), but it's like ignoring over 100 years of movies history just because one is too young to remember or luck of exposition ( older movies don't get the attention they deserve nowadays , with all the new , useless junk coming out ).
How can you ignore classics like Charlie Chaplin or Buster Keaton ?

The 80's for example were a golden era for funny movies, and a lot of legendary stars were borne ( too many to mention, but at the time Eddie Murphy was great and still funny, Jim Belushi, Chevie Chase, Bill Murray and so on...).

But without going to far back, one of the fairy recent movies that had me laughing my ass out was without shadow of a doubt KUNG FU HUSTLE.
I mean I watched that in original Korean with English subtitles and it made no difference, the movie was so cartoonishly funny that very little story was required to understand.
And at the end it was kind of sweet too ( involving a tender love story ) that after I cried for laughter the whole movie, I still had a couple of tears left for commotion at the end.
Thus , I declare KUNG FU HUSTLE one of the funniest movies EVER !

It's been a long, long time since I've last seen it, but I think I'll go for Spy Hard (1996). I remember not being able to sleep that night just because I was laughing all the time. That could also be because I was younger and had to laugh with sillier things, but I'll always say this one's my absolute favourite.